Capacitive touch sensors comprise a plurality of electrically conductive wires, electrically insulated from each other, and arranged to form a grid.
Capacitive touch sensors may employ the “self-capacitance sensing” technique wherein each sensing wire is connected to a controller configured to evaluate the capacitance value of each sensing wire, i.e. independently to each other. In these capacitive touch sensors, the controller is configured to detect the change of value in the capacitance of each sensing wire due to the parasitic capacitance provided by an object (e.g. a finger) touching the sensing wire. The position of a touch event is determined by the controller by detecting which sensing wires (i.e. which rows and columns) of the capacitive grid are touched, so that the position of the touch is determined as X, Y coordinates on the capacitive grid.
Some capacitive touch sensors employ the “mutual capacitance sensing” technique wherein the controller is configured to evaluate sequentially the mutual capacitance value at each intersection of sensing wires. In other words, the controller is configured to evaluate the capacitance value of each capacitor formed between sensing wires for each row and each column of the capacitive grid. A touch of an object (e.g. a finger) on the capacitive grid is detected as a change of value in the mutual capacitance.
Capacitive touch sensors embedded in a fabric are known. For example, US2016048235A1 discloses a fabric implementing a capacitive touch sensing comprising a plurality of electrically conductive wires, electrically insulated from each other, and arranged to form a grid.
Each wire is connected to a controller configured to evaluate the capacitance value of each wire (i.e. using the “self-capacitance sensing”). The controller detects the position of a touch event by detecting which horizontal wire and which vertical wire is touched, by detecting changes in capacitance of each respective wire of the capacitive grid. The controller uses the intersection of the crossing wires that are touched to determine the position of the touch event on the capacitive grid, so that the position of the touch is determined as X, Y coordinates on the capacitive grid.
The capacitive grid can be embedded in a fabric by using the electrically conductive wires as weft yarns and warp yarns. However, each electrically conductive wire of the capacitive grid (vertical and horizontal wires) have to be electrically connected to a sensing circuit by means of electrical contacts arranged along both the vertical side and the horizontal side of the capacitive grid. The routing of the electrical connections between the capacitive grid and the sensing circuit may be very complex when the capacitive grid has a great number of electrically conductive wires.
Furthermore, in case of a touch sensor having a substantially rectangular form (i.e. having a number of horizontal wires different with respect to the number of vertical wires) or provided with electrically conductive wires arranged parallel along only one direction (e.g. in case of a swipe sensor), the arrangement of the electrical contacts and the routing of the electrical connections between the conductive wires and the sensing circuit may be very difficult to be designed, making the production of the touch sensor complex and expensive and in some cases causing a stiffening of the touch sensor structure.